The primary modes of ground transportation include the automobile, motorcycle and bicycle. Each of these forms of transportation utilize a drive motor and a transmission to select one of a finite number of gears. This use of gears permits the vehicle to produce large amounts of pulling power when in a low gear, or travel at high speeds, when in a higher gear.
Although the gear system of transmissions are prevalent in ground transportation, there are a number of inadequacies associated with such systems. The main problem, is the finite number of gear ratios which are available for the vehicle. In many cases, it is not possible to adjust the vehicle to the specific gear ratio desired for a particular task. While bicycles are available in "10-speed" and "15-speed" models, motorcycles and automobiles do not typically have such capabilities. In addition, even with bicycles that have a large number of gears available, it is typically time-consuming to find the appropriate combination of rearward gears and forward gears to provide the desired gear ratio.